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In the present work, a combined process of laser powder bed fusion (LPBF) and hot working in terms of microstructure refinement was investigated for Fe-25Al-1.5Ta alloy samples. Uniaxial compression tests were carried out parallel and perpendicular to the building direction (BD) at 1000 °C, where BCC A2-phase was stable, at a strain rate of 0.0013 s−1. The true stress–true strain curves indicated a broad flow stress peak followed by a slight decrease, which is typical for dynamic recrystallization (DRX) of conventional BCC metals such as ferritic iron. A negligible dependence in the flow stress behavior on the compression direction was observed. DRX initiated at a stress of 18.7 MPa for the sample compressed parallel to the BD, corresponding to a true strain of 0.011, and at 18.1 MPa for the samples compressed normal to the BD, which corresponded to a true strain of 0.010. The microstructural investigations by electron backscatter diffraction (EBSD) showed that the relatively coarse and elongated grains of the as-LPBF builds were significantly refined after hot working. The microstructure of the compressed samples mainly consisted deformed grains. These were fragmented by sub-grains bounded by low-angle boundaries independent of the compression axis, indicating the occurrence of dynamic recovery (DRV) during hot working. In addition, a few equiaxed, small grains were observed in the pre-existing grain boundaries, which formed due to DRX. Most pores in the as-LPBF builds were closed after hot compression, particularly in the central region of the deformed specimens where the compressive stress state is dominant. In summary, hot compression reveals a practical thermomechanical post-processing treatment for Fe-Al-Ta iron aluminides built by LPBF. The hot working refines the epitaxially elongated microstructure of the as-LPBF builds by DRV/DRX and reduces the porosity.

Abstract. In the Laser Powder Bed Fusion (LPBF) process for metal components, a CAD file is sliced into layers with a thickness of 20-80 micrometers and the component is built up layer by layer. For this purpose, a metal powder layer is applied in each case and melted locally. This process is repeated until the geometry is completely established. The mechanical properties of the manufactured part are controlled by the cooling rate. It is currently not considered in the design of LPBF components, that the printed part has a varying heat flow into the surrounding powder and into the support plate depending on its slenderness. As a result of the different temperature histories, different microstructures with correspondingly different mechanical properties are formed in the untreated state (as-built). These differences must be considered in the component design. In this work, walls of various thicknesses were produced from 316L stainless-steel alloy using the LPBF process. The walls could be used to create plane-strain-compression-test specimens of various heights and orientations. The tests were performed according to Graf et al. [1] and the flow curve was calculated from the force-displacement curve while taking friction into account. Following that, tensile strength, Young’s modulus, yield strength, and yield stress were determined inversely. A clear dependence of the mechanical parameters on the degree of slimness was discovered, which was confirmed by microscopic examinations. To summarize, the plane-strain-compression-test is a quick and reliable method for determining the local variation of mechanical properties.